1. Field of the Invention
The present invention relates to impedance calibration, and more particularly, to an impedance calibration circuit used for calibrating an equivalent impedance of a semiconductor circuit element and method thereof.
2. Description of the Prior Art
Resistors are probably one of the most frequently used circuit elements in every kind of electronic devices. There are many types of resistors that can be selected when designing a discrete circuit. However, since passive resistors, such as metal or poly-silicon line resistors, occupy much area on an integrated circuit (abbreviated as IC), designers tend to use active elements to substitute for passive resistors when designing ICs, where a substitute active element has an equivalent impedance being substantially equal to that of a replaced passive resistor.
However, the characteristics of active elements are not only affected by manufacturing process variations, but the fluctuation of environmental parameters (such as temperature fluctuations) also changes the characteristics of active elements greatly. For example, when temperature changes, the equivalent impedance of an active element also changes accordingly. Under this situation the performance of an IC that comprises the active element would sometimes degrade considerably.